Three scientists who study the inner workings of cells have won the 2013 Nobel Prize in physiology or medicine for their work in unraveling the mystery of how proteins, hormones and other molecules are moved around inside cells and exported to other parts of the body.

The Nobel committee lauded Randy W. Schekman of UC Berkeley, Thomas C. Suedhof of Stanford University and James E. Rothman of Yale University for making known "the exquisitely precise control system for the transport and delivery of cellular cargo. Disturbances in this system have deleterious effects and contribute to conditions such as neurological diseases, diabetes and immunological disorders."

The announcement was made Monday in Stockholm.

"It's a fundamental discovery of cell physiology, and it was not entirely easy for these investigators when they started," Juleen Zierath, chairwoman of the committee that awarded the prize, said in an interview posted on the Nobel website.

For decades, the three molecular and cellular biologists have studied the cell's intricate internal transport system in which bubble-like vesicles shuttle key molecules including neurotransmitters and enzymes to different parts of the cell and through the cell's membrane.

"Think of a cell as sort of a factory, and it needs to produce proteins," said Zierath, a professor in clinical integrative physiology at the Karolinska Institute in Sweden. Cells "need to shuttle these proteins and cargo from one workstation to the next, so each protein can get a little bit better refined along the way."

The researchers had been considered among the top contenders for the award, which is worth about $1.2 million. Schekman and Rothman were joint winners of the prestigious Albert Lasker Basic Medical Research Award in 2002, and Suedhof was recognized with the award last month.

At a news conference in Berkeley, Schekman said he was aware of the speculation but didn't think he would win.

But hours after returning from an award ceremony in Germany, the 64-year-old was awakened at 1:30 a.m. by a ringing phone and his wife, Nancy, shouting, "This is it! This is it!"

"My heart was pounding and I was trembling," Schekman said. "But then I heard a comforting voice with a thick Swedish accent congratulating me."

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3 U.S.-based scientists win Nobel in physiology or medicine